Various types of radiation scintillation detectors are available for use in the detection of ionizing radiation. Although inorganic detectors tend to emit the most light when detecting radiation and generally have a light output which is linear with respect to the radiation, the inorganic detectors tend also to have a relatively slow response time and decay time thereby making it difficult to distinguish events. Often it is therefore preferable to use organic scintillator material when counting X-ray photons at high rates. However, organic radiation scintillation detectors tend to give off comparatively less scintillation light than the inorganic radiation scintillation detectors. This can pose a problem when fairly low energy level radiation, such as X-rays, is being detected by the detector. Therefore, when using an organic scintillator material, it is desirable that substantially all the light which is emitted be collected.
In Martinez, et al., "Effect of Crystal Thickness and Geometry on the Alpha-Particle Resolution of CsI (T1)", The Review of Scientific Instruments, pp. 974-977 (September 1960), the use of a single truncated cone crystal radiation scintillation detector is discussed. The publication states that if the crystal is beveled at the critical angle, any light originating in the light source area will strike the sides of the crystal at greater than the critical angle and will be internally reflected down through the bottom of the crystal. However, some of the emitted light will escape out the small planar surface on the end of the truncated cone opposite the end facing the photomultiplier tube. An early discussion of truncated conical plastic radiation scintillation detectors having sides which are surrounded with aluminum oxide or foil is contained in Hine, et al., "Conical Plastic Scintillators Show Total Gamma Absorption", Nucleonics, pp. 92, 94, 96, 98, and 100, (September 1960). This publication states that it is difficult to choose the best angle for a cone of given thickness.
Generally, coating the sides of a radiation scintillation detector with a reflector such as foil or aluminum oxide is not as efficient for reflecting light as total internal reflectance. In order to maximize total internal reflectance of scintillation light, the sides of the radiation scintillation detector may have to be beveled at a fairly extreme angle so that even the light emitted toward the top of the detector is totally reflected internally toward the bottom surface of the detector. Such single conical radiation scintillation detectors may be fairly narrow at the top and quite wide at the bottom. As a result, the light which is being transmitted through the bottom of the scintillator may be more diffuse.
U.S. Pat. Nos. 3,890,505 to Olson, 3,898,463 to Noakes, and 3,944,832 to Kalish all disclose cylindrical scintillation detectors which are coupled to photomultiplier tubes at both ends. The detectors are coated with a reflective coating or covering to reflect photon emissions internally.